diff --git a/include/constants/battle_config.h b/include/constants/battle_config.h
index 0831b93a3..29b7b5750 100644
--- a/include/constants/battle_config.h
+++ b/include/constants/battle_config.h
@@ -92,6 +92,9 @@
     #define GEN_8 5
 #endif
 
+// Mega Evolution settings
+#define B_MEGA_EVO_TURN_ORDER GEN_7 // In Gen7, a Pokémon's Speed after Mega Evolution is used to determine turn order, not its Speed before.
+
 // Calculation settings
 #define B_CRIT_CHANCE               GEN_7 // Chances of a critical hit landing. See CalcCritChanceStage.
 #define B_CRIT_MULTIPLIER           GEN_7 // In Gen6+, critical hits multiply damage by 1.5 instead of 2.
diff --git a/src/battle_main.c b/src/battle_main.c
index 5277ade1e..0c7f023bb 100644
--- a/src/battle_main.c
+++ b/src/battle_main.c
@@ -104,6 +104,7 @@ static void RunTurnActionsFunctions(void);
 static void SetActionsAndBattlersTurnOrder(void);
 static void sub_803CDF8(void);
 static bool8 AllAtActionConfirmed(void);
+static void TryChangeTurnOrder(void);
 static void CheckFocusPunch_ClearVarsBeforeTurnStarts(void);
 static void CheckMegaEvolutionBeforeTurn(void);
 static void CheckQuickClaw_CustapBerryActivation(void);
@@ -4688,10 +4689,37 @@ static void CheckMegaEvolutionBeforeTurn(void)
         }
     }
 
+    #if B_MEGA_EVO_TURN_ORDER <= GEN_6
+        gBattleMainFunc = CheckFocusPunch_ClearVarsBeforeTurnStarts;
+        gBattleStruct->focusPunchBattlerId = 0;
+    #else
+        gBattleMainFunc = TryChangeTurnOrder; // This will just do nothing if no mon has mega evolved
+    #endif  
+}
+
+// In gen7, priority and speed are recalculated during the turn in which a pokemon mega evolves
+static void TryChangeTurnOrder(void)
+{
+    s32 i, j;
+    for (i = 0; i < gBattlersCount - 1; i++)
+    {
+        for (j = i + 1; j < gBattlersCount; j++)
+        {
+            u8 battler1 = gBattlerByTurnOrder[i];
+            u8 battler2 = gBattlerByTurnOrder[j];
+            if (gActionsByTurnOrder[i] == B_ACTION_USE_MOVE
+                && gActionsByTurnOrder[j] == B_ACTION_USE_MOVE)
+            {
+                if (GetWhoStrikesFirst(battler1, battler2, FALSE))
+                    SwapTurnOrder(i, j);
+            }
+        }
+    }
     gBattleMainFunc = CheckFocusPunch_ClearVarsBeforeTurnStarts;
     gBattleStruct->focusPunchBattlerId = 0;
 }
 
+
 static void CheckFocusPunch_ClearVarsBeforeTurnStarts(void)
 {
     u32 i;